Recently, it has been shown that a mobile communication system may include a plurality of systems for covering identical service areas. For example, a TDMA voice communication system for transmitting voice signals and a TDMA packet communication system for data communication may be provided for the identical service areas. If the plurality of systems are provided for the identical areas in the conventional mobile communication system, communication requests from the mobile stations are notified by the individual systems. Meanwhile, the mobile stations, which are provided with a plurality of receivers corresponding to the systems, receive communication requests from the systems individually, and enjoy communication services from the systems respectively.
As described above, if the mobile station in the conventional mobile communication system is to enjoy communication services from the plurality of systems, the mobile station may by provided with a plurality of receivers corresponding to the systems so as to receive communication requests from the systems, simultaneously. Such a situation is problematical by causing difficulty of miniaturization of the mobile station, and by causing enlargement of power consumption.
The problems described above may occur similarly concerning the level measuring channels utilized for the plurality of systems. The details are the following. A fixed station, in a mobile communication system coming under the minimum zone structure TDMA system, is generally provided with a level measuring channel having a constant transmission power in all slots. The mobile station measures reception field levels of a plurality of level measuring channels and visits the zone corresponding to the channel having the highest electrical field power level.
Incidentally, it is difficult to determine the zone to be visited by measuring electrical field power levels of ordinary traffic channels in place of the level measuring channel. The reason is that transmission power control for varying transmission power is executed, with respect to every mobile station (i.e., every TDMA slot), in order to reduce interference with other zones, so that the zone cannot be determined simply by the reception field levels of the traffic channels.
However, since the master and slave systems are provided with independent level measuring channels in the conventional technique, which causes difficulty such as miniaturization of the mobile station and enlargement of power consumption. Furthermore, communication quality is reduced due to increasing of interference for traffic channels in other zones, the channels having the same frequency of the level measuring channel.